1. Field of the Invention
The present invention relates to a dispersion strengthened copper alloy and a method of manufacturing the same, wherein particles are dispersed in a copper matrix, and, to various applications of this dispersion strengthened copper alloy.
2. Description of the Related Art
There is now an increased demand for an copper alloy having both a high electric conductivity and a high mechanical strength, which is applicable to a coil material for generating a high magnetic field, a semiconductor lead frame, or a spot-welding electrode. However, it is very difficult to obtain a copper alloy having a high electric conductivity and a high mechanical strength, which are incompatible with each other.
There is known a dispersion strengthened copper alloy in which dispersion particles are dispersed in a copper matrix, as a copper alloy having relatively high electric conductivity and mechanical strength. In this dispersion strengthened copper alloy, very fine particles are uniformly dispersed in a copper matrix in order to attain the two incompatible characteristics.
As a method of manufacturing the dispersion strengthened copper alloy, there is known a technique wherein powder for copper matrix and powder for dispersion particles are pulverized and mixed by using a mixer such as a ball mill. However, in the case of the dispersion strengthened copper alloy, it is very difficult to disperse the dispersion particles finely and uniformly by this method. Consequently, the obtained copper alloy has a low strength.
As another method of manufacturing the dispersion strengthened copper alloy, there is proposed an internal oxidation method (USP 3,779,714). In this method, powder of an alloy consisting of copper and an element which is more easily oxidized than the copper are heated in a oxidizing atmosphere, and the surface area of the powder is oxidized. The oxidized powder is sealed in a container and heated, so that oxygen existing in the surface area of the powder is diffused inwards. Thus, powder of an alloy, in which oxide particles of the added element are internally dispersed, can be obtained. According to this method, a dispersed strengthened copper alloy in which fine dispersion particles are uniformly dispersed in a copper matrix can be obtained.
In this method, however, a very long time is taken in the internal oxidation process in which the oxygen existing in the surface area of the alloy particles is diffused inwards and the added element is completely oxidized. Thus, part of the added element is not oxidized and may remain in the copper matrix as a solid solution element. If the part of the added element remains in the copper matrix as the solid solution element, the electric conductivity of the dispersion strengthened copper alloy is considerably lowered. If an amount of the dispersion particles is decreased so as to increase the electric conductivity, the strength of the alloy is lowered.
As still another method of manufacturing the dispersion strengthened copper alloy, there is known a mixed oxide reduction method, which is described, for example, Trans. AIME, vol. 218 (1960), p. 775, Lecture of Powder Metallurgy Technique No. 9, ed. Shadan-hojin Powder Metallurgy Technique Association, Powder Metallurgy Applied Product (IV)--Special Material--(1964), p. 6, Nikkan Kogyo Shinbunsha Shuppan, or Published Unexamined Japanese Patent Application (PUJPA) No. 62-93321. In this method, a metal oxide of a matrix and raw material for dispersion particles are pulverized and mixed. In the resulting mixture, only the metal oxide of the matrix is reduced, and a mixture of a metal and dispersion particles is prepared. Thereafter, the mixture is sintered by a normal powder metallurgical method, thus obtaining a dispersion strengthened alloy.
The mixed oxide reduction method is advantageous only where it is applied to the manufacture of a dispersion strengthened alloy, the matrix of which is formed of nickel or silver. However, when this method is applied to the manufacture of a dispersion strengthened copper alloy wherein a copper oxide is employed as a oxide for a metal matrix, it is difficult to uniformly disperse fine dispersion particles in the matrix. Thus, this method is unsuitable for obtaining a high-strength dispersion strengthened copper alloy.